US3021864A - Pipeline - Google Patents

Description

F- S. YOUNG Feb. 20, 1962 PIPELINE 2 Sheets-Sheet 1 Filed May 2, 1958 CURRENT yaw w ki' W A TTOR/VEVJ' Far/v /e J. you/79 Feb. 20, 1962 F. s. YOUNG PIPELINE Filed May 2, 1958 2 Sheets-Sheet 2 Far/v /e J. Ve a/79 INVENTOR.

Uflitfid t t t n 3,021,864 a PIPELINE Farrile S. Young, Houston, Tex., assignor to Gulf-Interstate Oil Company, Houston,- Tex., a corporation of Delaware 1 Filed May 2, 1958, Ser. No. 732,497 4 Ciaims. (Cl..137236) This invention relates to pipelines and 'more particularly to pipelines crossing very deep bodies of water.

Pipelines have been laidin shallow water. These lines 3,021,864 V Patented Feb. 20, 1962 I service, should the occasion arise.

are usually weighted and rest on bottom. Frequently they are buried in the soil below the body of water. This conventional practice cannot be followed. in deep water such as the Yucatan Straits, Mediterranean, etc. because of the many problems encountered in deep water. For instance, the crushing pressure of waterat great depth ishigh. This pressure'varies with the contour of the bottom and would require the line to bede'signedzfor the greatest depth expected. In-the Yucatan Straits this would be in the order of 6,700 ft. is approximately 3,000 psi. crushing pressure which would require A inch wall thickness when using grade B 12-inch pipe with a nominal safety factor of 1.25. Very high stresses wouldbe caused in suspending long lengths 'of such pipe o'fl of a laying'barge to the'bottom Bending forces many times the yield strength of the pipe" would be developed. The high bending forces could' onlybe eliminated by utilizing a fleet of crane barges. Keeping these barges effective-in the surface'currents such as the six mile per hour current in the. Yucatan Straits would be a very difficult assignment. 'Additionally, large bending forces would be developed due. to the pipe conforming to the unknown roughness of the." bottom. In many cases sharp cliffs are present in deep water which are hard to detect and'avoid. Long spans of pipe over the sharp depressions could cause suflicie'nt forces to kink the pipe, with possible rupturing occurring."- Another'factor to consider in'deepwater is high oscil-' lating forces near the bottom. These forces place high strains on the pipe especially when rigi'd pipe spans sections of the bottom and is anchored at each' end by silt. In the event of sudden rough water great difliculty would be experienced inreleasing and later reclaim ing a pipeline. Picking a pipe ofi of the bottom of 6,700 ft. of water without kinking it would be an expensive time-consuming job, if evenpossible.

It is an object of this invention to provide a pipeline for crossing deep bodies of water. i v Another object is.to provide a pipeline which is below the level of the surface but which is above bottom where uncontrollable .scouring, spans, sharp bends and high oscillating'forces can occur.

Another object is to provide a pipeline for deep water which is maintained at a uniform controlled depth that will fit the crushing strength of the pipe wall. 7 I 1 Another object is to provide a pipeline having flexible connections at spaced points to allow the pipeline to move with the variable currents which are encountered and keep the stress level of thepipe at a relatively low point. v Another object is to providea pipeline suspended at an intermediate level in a body of water in which the stress level of the pipe due to the means for anchoring the pipe in position is at-a relatively low value.

Another object is to provide a pipeline for suspending at an intermediate level in a body of water which is compartmented to prevent the line from sinking to bot tom should a break occur.

Another object is to provide a marine pipeline in which each section may be pressured and tested before it is lowered into final position. I I

At this depth there.

designed with buoyancy.

Another object is to provide a pipeline for marine service in which a thinner wall pipe can be used for a particular service as compared to a pipe designed for laying on bottom. y

In accordance with this invention the pipeline is It is anchored in place with a plurality of anchors which are upstream of the pipe a considerable distance and connected to. the pipe by cable. The normal currentwill cause the pipe to sink to a predetermined level. A second anchoring system is provided which limits" the level to which the pipeline testing of sections of the line as it is being laid and prevent flooding of the entire line in the event of a leak after the line has been put in service.

" lifeferring now'to the drawings wherein there is shown an illustrative embodiment of this invention and wherein like reference numerals indicate like parts:

FIGURE 1- is a cross-sectional view illustrating a pipeline suspended at an intermediate level and crossing a deep body of water;

'FIGURE 2 is a sectional view taken at right angles to FIGURE -1 and showing three different positions of the pipelineunder three different current conditions; and FIGURE 3 is aperspectiveview of the pipeline and anchoring system.

The pipeline indicated generally at 10 is made up of a plurality of-"sections'; someof which are shown at '11,? 12, 13 and 14. Each sectionof the pipeline is fabricated in the conventionalmanner by welding together short lengths of pipe.

At periodic intervals .the sections of the pipeline 10 are connected together by flexible connectors 15. Theseconnectors permit thesections of pipe to bend relative to each other and move with the-variable currents which are encountered. The flexibility provided by connectors 15' keeps the stress level inthe relatively rigid pipe at safe levels. Tht-flexible connections permit the laying The number of flexible connectors 15 employed will preferably be kept to a minimum, but as many as necessary to give a line the desired flexibility maybe 1 d Thepipeline 10' compartmented by a plurality of check valves-16 which control flow through the'pipeline and are preferably spaced along its entire length. These check valvespermit fiowfrom the source of the fluid to' be pumped to'its destination or te rmina1.-'-- The check valves are preferably positioned every half mile or so a ;exerted by the water surrounding the line. Thus if'a break occurs, the downstream check valve will be immediately closed by the high pressure in the line downstream of the valve.- The terminal outlet from the line would of course be closed' upon a break occurring to trap this high pressure within the line and prevent flooding of the line downstream of the break. The line would be closed ofi at its upstream endto permit gas pressurew'ithin the upstream section of the line to bleed down. As soon as this pressure is reduced below the hydrostatic pressure of the surrounding water, the upstream yalye adjacent a break would close. Thus, only the section ofpipe between .two adjacent check valves would flood, .and the buoyancy of the remainderof the pipe would prevent .the entire pipeline from sinking. Of course the .buoyant'pipeline would tend to supp rt the section which had filled with water until the leaky section could .be repaired.

The pipeline is anchored in position with a system of anchors which maintain the pipeline between ,a ,prede.

termined high and low level beneath the surface of ,the water. In straits and narrow seas for which this pipeline is eminently suited, arather constant currentis usually present. In designing the pipeline, this current .is taken into consideration. The buoyancy of the pipeline and necessary crushing strength of the pipe andpermit use of a thinner wall pipe. Thin wall pipe is less expensive and gives higher buoyancy. The high buoyancy is used to minimize the length of the primary anchor lines. Thus, a compromise depth must be selected. ,For instance, in the YucatanStraits which are some 6,500 ft. in .depth, a compromise pipe depth of 51,500 ft. ,may be selected. Current at this depth .is normally 1.12 miles per hour. The tangent of .the angle which the pr m iy anchoring line would assume is the buoyancy forces .of the ,pipeline divided by the current forces .on the pipeline. Given this angle and the height of .the pipeline, the length of the primary anchoring line may be calculated with :simple trigonometry. For instance if we assume .a pipeline having approximately 14 lbs. per ft. of buoyancy submerged ,at 1,500 ft. in the Yucatan Straights, the tangent of -14 diyided by current forces (which with 12 inch pipe would result in 27.5 lbs. per it.) would be 27 degrees. 'By simple trigonometry the length of the primary anchor line would be approximately 11,000 it.

A plurality of primary anchor lines are indicated at 17 and extend between the pipeline .10 and a plurality of anchors 1E8 positioned upstream from the pip line. It will be understood that the lines 17 and anchors 1.8 will hold the pipeline ubmerg at approximat l 1,500 ft.

due :to't-heforceof the 1.12mile perhour current. If the current increases above ,this value, the pipeline would doscend. Upon decrease in current, the pipeline will ascend. Pref rably the system should be designed with the maximum current conditions in mind so :that the wall thickness of the pipe selected will be .suthcient to withstand the crushing pressure at the design depth for maximum current. v

It :will be noted that the length of'the anchor .line 17 is substantially greater than the depth of the water and, therefore, under conditions of no current flow .or substantially no current flow, the pipeline could rise to the surface where it would be .a menace to navigation. To establish an upper limit for the pipeline, .a secondary anchoring system is provided. This system includes the anchors 19 to which the secondary anchoring cables 20 at attached. These cables 20, li-mit the upward rise of the pipe to some preselected value, such as 3.00 ft. below extend between the respective anchors 18 and 19 and a common point 21 at which they are 'joined together. A

single cable 22 extends from this point of joinder to the pipeline :10.

In order that the lines 20 be as short as possible, the point 21 is selected at maximum distance from the pipeline 110. ;For :instance with the cable 17 extending. at an angle :of 27 degrees, the point 21 could be approximately 2,200 ft. from the pipeline and cable '20 would have a length of' approximately 4,000 ft; A further advantage of this system is that a single line to the pipe cannot set up opposing stresses. Where two cables :are

I attached to the pipe at .or close to each other, opposing stresses are possible.

The dead weight of cables 17, 20 and 22 will'be considerable and if supported by the pipe would cause 'it to assume'a configuration resembling a succession of arcs. This isundesirable, as stresses in the ,pipe should ,bemaintained at a minimum. Therefore, it is preferred to provide the cables with asystern ,of floats which will sup ort the dead weight of v the cables. Such a system of jfioats maybe provided by floats 23 attached to points 21 and heats 24 attached to cables .22 immediately adjacent the pipeline 1.0.

Laying procedure would preferably be ,to start from the terminal end and build toward the'source so that each section -of pipe could be tested by compression on the lay barge. ,In performing these tests the several check values .16 would provide test compartments as they would close against new away from the terminal end of the pipe.

,As each section .of pipe is laid, a pair of .lay barges would drop each pair of anchors 18 and 19 at points the surface, ,as' bestshown in FIGURE 2. For this purspaced apart by the approximate distances which these anchors should assume with each other. However, it will be apparent that forces to which the pipeline will be subjected .and other factors, such as bottom conditions, difficulty in positioning the vessels, etc., will result in dragging of some of the anchors until all of the primary anchors :18 .are cfiective :to hold the pipeline in position. 01? course as the anchors 18 drag, they will move closer to anchors 19, and these anchors will assist in holding the pipeline 10 in pos'iton. This condition is shown by :one of the anchoring systems of ,FIGURE ,3. This is of partic lar advantage in the event of unusual conditions which might tend to drag one or more of anchors l8.

.Afterthe line has been laid, it should assume the-P ition shown at A of FIGURE 2. However, if the normal currents reduce, the line will ascend from the position .A and upon a substantially no current condition existing, the pipeline will move to position C. Upon the normal currents increasing, the pipeline will descend toward position B. Position B represents the depth to which the pipe will descend with maximum current conditions. It is of course apparent from FIGURE 2 that the primary anchoring cable 17 is controlling the position of the pipeline at positions A and .B, and that the secondary anchoring cable .20 is controlling the position of thepipcline at P sition (1.

The depths given in FIGURE 2 are suggested for a bodyof water 6.5.00ft. deep.

From the above it will be seen that the-objects of this invention have been attained. There has been provided a system .of suspending pipe at an intermediate level in deep water, and the pipe has been protected against com plete submergence even :in the case of leaks. As compared to .the pipe resting on bottom, a much thinner wall. pipe-may he used. It .will beappreciatedthat while in buoyancy. If the line is to transmit liquid, auxiliary means would have to be provided to render the pipeline negatively buoyant.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made Within the scope of the appended claims Without departing from the spirit of the invention.

What is claimed is:

1. A pipeline suspended under water comprising, a plurality of sections of metallic pipe, a plurality of flexible connectors connecting the pipe sections into a continuous pipeline, said pipeline being puoyant when containing gas, primary anchoring means provided by a plurality of primary cables secured to the pipeline at spaced points and to -a plurality of primary anchors resting on bottom upstream of the pipeline, said primary cables being of greater length than the Water depth, the length of the primary cables and the degree of buoyancy of the pipeline being selected relative to the maximum current conditions expected to provide a predetermined depth beyond which the pipeline will not descend, and secondary anchoring means provided by a plurality of secondary cables secured to the pipe at spaced points and to secondary anchors resting on bottom, said secondary cables being of lesser length than the depth of the water to limit ascending of the pipeline toxa predetermined depth as the force of the current reduces.

2. The pipeline of claim 1 wherein means are provided for supporting the dead weight of both primary and secondary cables to prevent this weight from being imposed on the pipeline.

3. The pipeline of claim 1 wherein a plurality of check valves are positioned at spaced intervals in said pipeline to permit testing of sections of pipe as they are assembled and to compartmentize the line in the event of a leak to prevent flooding of the entire pipeline.

4. A pipeline suspended under water comprising, a plurality of sections of metallic pipe, a plurality of flexible connectors connecting the pipe sections into a continuous pipeline, said pipeline being buoyant when containing gas, and means for anchoring the pipeline in position and maintaining the pipeline below a predetermined depth While permitting the pipeline to descend between said depth and a second predetermined depth upon an increase in speed of water currents including primary and secondary cables and anchors, said primary and secondary cables provided by separate cables commencing at the respective anchors and extending to points of juncture and by common cables extending from the points of juncture to the pipeline.

References Cited in the file of this patent UNITED STATES PATENTS 486,986 Schinke Nov. 29, 1892 1,956,010 Diescher Apr. 24, 1934 FOREIGN PATENTS 2,141 Great Britain Aug. 21, 1866 80,240 Denmark Nov. 21, 1955

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